Pension and Other Postretirement Benefits Costs - Narrative (Details) - USD ($) $ in Thousands	2 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 22, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year	6.75%	6.75%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.75%	4.75%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate		2025
Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan Net Periodic Benefit Costs Overhead Charge Percentage		25.00%
Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan Net Periodic Benefit Costs Overhead Charge Percentage		35.00%
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan Assets, Amount	$ 257,797	$ 257,797	$ 287,925
Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Accumulated Benefit Obligation	385,900	385,900	410,300
Non-Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan Assets, Amount	0	0
Defined Benefit Plan, Benefit Obligation	35,400	35,400	36,600
Northwest Natural Gas Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan Amounts That Will Be Amortized From Accumulated Other Comprehensive Income Loss In Next Fiscal Year Regulatory		13,700
Defined Benefit Plan Amortization Of Net Gains Losses Regulatory		14,200
Defined Benefit Plan Amortization Of Net Prior Service Cost Credit Regulatory		(500)
Settlement expense	(600)	(600)
Payment for Pension and Other Postretirement Benefits		15,540
Defined Contribution Plan, Cost		6,500	5,400	$ 4,600
Northwest Natural Gas Company [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan Assets, Amount	257,797	257,797	287,925	257,714
Total Pension Asset Investments Net Of Receivables And Payables	257,796	257,796	287,895
Defined Benefit Plan, Benefit Obligation	455,568	455,568	486,289	457,839
Payment for Pension and Other Postretirement Benefits		17,715	21,483
Expected future employer contributions	13,318	13,318
Northwest Natural Gas Company [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan Assets, Amount	0	0	0	0
Defined Benefit Plan, Benefit Obligation	28,172	28,172	28,927	29,395
Payment for Pension and Other Postretirement Benefits		1,674	1,737
Expected future employer contributions	1,787	1,787
Northwest Natural Gas Company [Member] | Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(162,400)	(162,400)
Plan Assets, Amount	257,800	257,800	287,900
Defined Benefit Plan, Benefit Obligation	420,200	420,200	449,700
Expected future employer contributions	11,000	11,000
Northwest Natural Gas Company [Member] | Western States Office and Professional Employees Union Pension Fund [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer Plans, Withdrawal Obligation	6,813	6,813			$ 8,300
Multiemployer Plans, Plan Contributions		600
Multiemployer Plan, Contributions by Employer		$ 600	600	600
Northwest Natural Gas Company [Member] | Western States Office and Professional Employees Union Pension Fund [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer Plan, Collective-Bargaining Arrangement, Percentage of Contributions Required for Multiple Collective-Bargaining Arrangements		4.00%
Northwest Natural Gas Company [Member] | Western States Office and Professional Employees Union Pension Fund [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer Plan, Collective-Bargaining Arrangement, Percentage of Contributions Required for Multiple Collective-Bargaining Arrangements		6.00%
Northwest Natural Gas Company Consolidated [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement expense	0	$ 0	0	(193)
Additional Amount Authorized for Inclusion in Rates	8,100
Northwest Natural Gas Company Consolidated [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement expense	$ 0	$ 0	$ 0	$ 0